“During the 1.x timeframe, changes should primarily be additive, giving developers confidence that the language will not continually shift beneath them.”
Mojo reaches 1.0 with the compiler still closed and the open source release promised for 2026, which is the same promise from three years ago with the year swapped out. The stability guarantee is that changes will be “primarily” additive. That word is carrying the whole sentence. The standard library is open and took 1,100 community pull requests, which is a good way to get people building on a toolchain one company owns outright.